Generally (see FIG. 1), a rock drill rig comprises a movable carrier 1, a boom 2 and a feed beam 4 connected to the boom 2 via a feed beam holder 3. The feed beam 4 and the feed beam holder 3 are movable in relation to each other along at least part of the length of the feed beam. A drilling machine 5 is movably arranged on the feed beam 4.
One of the most important features of a drill rig is its durability and reliability. All parts of the equipment need to answer to the high demands that are required in the extreme working operations of a drill rig. It is also important that its accuracy can be withheld under these conditions. Therefore, improvements that ameliorate the endurance, accuracy and reliability of the equipment is always sought for. One of the parts that are put under a lot of stress is the feed beam 4.
From EP 0 159 974 B1 it is known to use an extruded light metal feed beam on a drill rig, which feed beam includes guides for guiding a rock drill. An extruded feed beam of light metal has the advantage of being both lighter and straighter than a conventional steel beam. Additionally, there exists a bigger liberty in the design of the extruded aluminium feed beam than for a conventional steel beam. A disadvantage is that aluminium is weaker than steel and that the feed beam has to be made thicker than a conventional steel beam. The feed beam used in EP 0 159 974 B1 is of the open, channel beam type.
In the international patent application No PCT/SE2006/000244 a novel arrangement with a pressure cylinder inside the feed beam provides for the possibility to use a closed box beam instead of a conventional open channel beam.
The closed feed beam of the box beam type is advantageous as it has a higher structural strength than the open channel beam of a corresponding thickness. It can therefore be made both lighter and stronger than a conventional feed beam.
It is suggested on the Internet home page of Doofor rock drills (http://www.doofor.com/products/feedbeam.htm) available on Jun. 29, 2005, that closed, so called box beams may be used as aluminium feed beams. The feed beam presented on the Doofor home page is only a schematic illustration showing only a few constructional details.